By Zach Spear

Published: 09:00 AM EST

Psystar has finally scored a victory in its defense against Apple as the two sides prepare for trial, but that win also comes at a small cost for the Mac clone maker.

According to an 8-page order filed late last week, Florida-based Psystar will be permitted to answer Apple's lawsuit by using copyright misuse in its defense. Apple sued Psystar last July, and the Open Computer maker has been tinkering with its counterclaims since August.

Psystar previously claimed anti-trust violations, but Judge William Alsup threw that argument out.

Now, the company alleges Apple "wrongfully extended the scope of its Mac OS copyright" through the End User License Agreement, which requires installation only on Apple computers and causes the OS to malfunction if disobeyed.

After Apple requested to have that argument thrown out as well, Psystar restated its case in a 17-page filing that the judge's most recent order responds to.

The defendants accuse Apple of improperly making claims under the Digital Millennium Copyright Act (DMCA), extending the Mac OS copyright into the computer hardware market by "intimidating potential competitors."

Apple argued Psystar's counterclaim is invalid because copyright misuse can only be alleged as a defense, not a counterclaim, but Judge Alsup disagreed.

"This order is unconvinced, however, that misuse may never be asserted as a counterclaim for declaratory relief," the judge wrote. "PsyStar may well have a legitimate interest in establishing misuse independent of Apple's claim against it, for example, to clarify the risks it confronts by marketing the products at issue in this case or others it may wish to develop."

Judge Alsup added that if misuse is proven, it would "bar enforcement" against Psystar and other potential defendants with similar interests. Apple had cited previous cases where copyright misuse could only be used as a defense; however, Alsup ruled in this particular case, misuse is in play because Apple has itself asserted copyright claims against the defendant.

Just because Apple's interpretation of its rights could end up being correct doesn't prevent Psystar from arguing otherwise, the judge said.

"Apple responds that it is within its rights to determine whether, how or by whom its software is reproduced and how it is to be licensed, distributed or used," wrote Judge Alsup. "This may ultimately prove to be true. Apple, however, identifies no reason to bar the claims as a matter of law at the pleading stage. This order declines to find the claims futile."

However, the ruling wasn't a total loss for Apple. The judge denied a part of Psystar's proposed counterclaim based on state unfair competition laws.

"[Psystar] fails to explain, however, how this conduct constitutes harm to competition or a violation of the spirit of the antitrust laws," he wrote. "[Tying copyrights to computer hardware] requires monopolization. PsyStar has identified none."

The judge instructed both parties to take discovery and prepare themselves for trial and/or summary judgment.

The trial is scheduled to begin on Nov. 9.